code: def test_encoding_new_categories(df_enc):
      df_unseen = pd.DataFrame({"var_A": ["D"], "var_B": ["D"]})
      encoder = OrdinalEncoder(
          encoding_method="arbitrary", unseen="encode"
      )
      encoder.fit(df_enc[["var_A", "var_B"]])
      df_transformed = encoder.transform(df_unseen)
      assert (df_transformed == -1).all(axis=None)
  
file_path: feature_engine/tests/test_encoding/test_ordinal_encoder.py
imports: import numpy
  import pandas
  import pytest
  from feature_engine.encoding import OrdinalEncoder
label_desc: Use image node_id 15 for calling a global function with example usage: test_encoding_new_categories(df_enc) without return types